Some Great Questions from the audience which I’ll try to summarise here

Q: What is the maximum recommended CPU limit to decide what SQL Servers to virtualise? In Hyper-V this is an easy question to answer as it only supports 4. VMware supports more cores, BUT the general recommendation is NOT to use more CPU’s than are available on a single NUMA node which is either 4 or 8. The reasoning is that your virtual operating system will not be “NUMA aware” and having some of the CPU’s on one NUMA node and some on another will be very expensive. There is not a lot of research yet on this type of scenario, so most people avoid it. Your mileage may vary, but we avoid crossing NUMA boundaries with virtualisation.

Q: Does the MAP tool account for growth ?

No, it only captures a snapshot of resource usage. My concern is not usually the growth in CPU usage and IOPS of workloads, but the fact that as time goes on MORE workloads will be added to the virtualised environment. You need to figure out what spare capacity will be allocated for this on the virtual hosts in terms of CPU, IOPS and disk space.

How much disk space you need to park for “growth” depends on how you are virtualising. If you are only moving physical SQL Servers and moving drives like for like, then they may already have had capacity planning for X time.

If you are doing SQL consolidation (moving data and log files to new environment), then this is trickier. It is possible to run the MAP Inventory tool at different months to measure % growth in databases to help plan for growth.

Q: Why don’t we ask for IOPS based on the MAX amount used.?

This would be cool to do for only one server as you get guaranteed performance no matter how busy it is! However imagine you have 100 servers each doing an avg 50 IOPS, 80% percentile at 80 and a max 250 IOPS.

Commissioning 25,000 IOPS at 8ms could be quite expensive, but 8,000 iops might be more practical.

Note we are not saying that the maximum IOPS we would ask for is 8,000. Just that we want 8,000 at avg 8ms latency. Hopefully the storage will be able to spike above 8,000 IOPS.

Its unlikely that all 100 servers will need their “max” at the same time, so we can save some costs with shared storage.